(Kaichu type submarine scanned from "Submarines of the
Imperial Japanese Navy" by Polmar and Carpenter)
IJN Submarine RO-50:
Tabular Record of
© 2001-2016 Bob Hackett & Sander Kingsepp
18 February 1943:
Tamano. Laid down at Mitsui Zosensho as
a 960-ton type K6
27 November 1943:
Launched and numbered RO-50.
5 June 1944:
LtCdr (Cdr, posthumously) Kimura Masao (63)(former CO
of I-159) is appointed Chief Equipping Officer.
31 July 1944:
Completed and attached to Maizuru Naval District. LtCdr
Kimura is the Commanding Officer. Assigned to SubRon 11 for training and work-up.
20 October 1944: American Operation "KING TWO" - The Invasion of Leyte,
Admiral (later Fleet Admiral) William F. Halsey's (USNA '04)
Third Fleet of 738 ships including 18 aircraft carriers, six battleships, 17
cruisers, 64 destroyers and over 600 support ships land the Army's X Corps (24th
Infantry and 1st Cavalry Divisions) and the XXIV Corps (7th, 77th and 96th
Infantry Divisions) that begin the campaign to retake Leyte.
5 November 1944:
Reassigned to SubDiv 34 in Vice Admiral Miwa
Shigeyoshi's (39)(former CO of CL KINU) Sixth Fleet (Submarines).
19 November 1944:
Departs Kure on her first war patrol for an area E
22 November 1944:
Philippine Sea. En route, RO-50 is attacked by a
IJNAF floatplane that drops two depth-charges. The submarine dives to 130 ft
to escape damage.
25 November 1944:
150 miles NE of Lamon Bay, Luzon, Philippines.
RO-50's Type 13 air-search radar detects a plane, presumably launched from a
carrier. LtCdr Kimura commences a chase. Five hours later his sonarman detects
screw noises. Soon thereafter, three carriers and eights destroyers are sighted,
steaming in a ring formation. 
RO-50 continues her approach and penetrates the escort screen. Suddenly,
Kimura sights a WASP-class carrier dead ahead, 875 yards away! He fires a
four-torpedo salvo at the carrier and submerges to 263 feet. A massive explosion
follows. Five minutes later the sonar operator reports breaking-up noises that
continue for the next two minutes.
Later, LtCdr Kimura reports sinking an American escort carrier and a
destroyer (not confirmed postwar).
27 December 1944:
Returns to Kure.
9 January 1945: American Operation "MIKE ONE" - The Invasion of Luzon:
Vice Admiral (later Admiral) Thomas C. Kinkaid's (USNA '08) Task Force 77
lands almost 175,000 men of LtGen (later Gen) Walter Krueger's Sixth Army at
Lingayen Gulf, Philippines under the cover of Vice Admiral (later Admiral) Jesse
B. Oldendorf's (USNA '09) TG 77.2 bombardment force and aircraft of Rear Admiral
(later Vice Admiral) Calvin T. Durgin's (USNA '16) TG 77.4. The Sixth Army
begins a campaign to retake Luzon from General Yamashita Tomoyuki's 14th Area
23 January 1945:
Departs Kure for the area E of Luzon on her second
war patrol. Vice Admiral Miwa and his staff arrive to see RO-50 off.
1 February 1945:
Leyte, Philippines. LtCdr Kimura sights an unescorted
target and gives chase, but it turns out to be a hospital ship.
3 February 1945:
E of Luzon. RO-50 is briefly chased by an American
anti-submarine vessel. RO-50 escapes, but is damaged. 
4 February 1945:
Vice Admiral Miwa gives orders for RO-50 to stand by
to rescue naval pilots from Batulinao, Philippines.
10 February 1945:
Off the east coast of Mindanao, Philippines. Around
0810, LtCdr Kimura fires a four-torpedo salvo at a convoy sailing in a single
column at 08-01N, 136-37E. The 3,640-ton Landing Ship Tank LST-577 is
proceeding from Hollandia, New Guinea to Lingayen Gulf, Luzon Island, in a
convoy on a resupply run. At about 0810, two torpedeos pass through the convoy
from port to starboard and one hits the LST-577, blowing about 1/3 of the vessel
clean off. A total of 166 sailors and passengers are lost, including LST-577's
skipper, Lt. Carl H. Stahl.
USS LtCdr Louis E. Schmidt's ISHERWOOD (DD-520), supported by HAAS (DE-424),
COOLBAUGH (DE-217) and SC-1012 commences a box search. SC-1012 first makes a
contact with a submerged target and attacks it with nine Mk.10 "Hedgehog" projector
RO-50 surfaces after sunset. At 2110, ISHERWOOD makes radar contact on a
surfaced sub at 14,000 yds. The destroyer goes to General Quarters and rings up
turns for 25 kts. At 1500 yds, first her starboard and then the port searchlight
is turned on, but neither can bear.
LtCdr Kimura sights an enemy destroyer illuminating his submarine from
the port quarter direction and crash-dives to 395 ft. ISHERWOOD soon picks up
RO-50 on her sound gear and drops a full pattern of depth charges at a shallow
setting. The explosions rupture RO-50's diving tank valves and shatter the lenses
in both periscopes. All of RO-50's torpedo tubes develop leaks. After ISHERWOOD
drops two additional patterns, several sailors including her skipper report
smelling oil. After a third run, the destroyer is unable to regain contact.
After escaping, RO-50 surfaces. A 40-lb depth charge fragment is
recovered from her afterdeck. LtCdr Kimura reports sinking an American cargo
11 February 1945:
ISHERWOOD scuttles the wreck of LST-577 E of
Mindanao at 08-05N, 126-17E.
14 February 1945:
LtCdr Kimura sends a situation report to Sixth
Fleet HQ. He receives permission to return to base after reconnoitering the
Nansei Shoto area.
19 February 1945:
S of Kyushu. The Kure-bound RO-50 is attacked by
an IJNAF seaplane that drops three depth charges.
20 February 1945:
Returns to Kure. Later, she is transferred to
2 April 1945:
Lt (later Vice Admiral, JMSDF) Imai Umeichi (67)
(former torpedo officer of I-8) is appointed CO.
20 April 1945:
Departs Maizuru on her third war patrol. Proceeds
through Bungo Suido Channel heading for the Kita-Daito-Jima area.
28 April 1945:
Off Kita-Daito-Jima Island. RO-50's sonar operator
detects screw noises of a task force but the distance is too great for an
4 May 1945:
Returns to Kure, later proceeds to Maizuru.
29 May 1945:
Departs Maizuru for East China Sea on her fourth war
6 June 1945:
Arrives at her assigned area E of Taiwan. She is next
redirected to an area between Ulithi and Okinawa.
3 July 1945:
Returns to Maizuru.
11 August 1945:
Departs Maizuru for Dairen to refuel there and then
operate in the Okinawa area.
15 August 1945:
Dairen roadstead. Early in the morning air raid
warning is given and RO-50 dives to escape the bombing. After surfacing at 1500
Imai is informed about Emperor Hirohito (Showa)'s Imperial Rescript broadcast
calling for an end to the hostilities.
That same day, SubDiv 34 is disbanded. RO-50 is reassigned to SubDiv 15.
Departs Dairen for Maizuru.
Late August 1945:
Returns to Maizuru, later transferred to Kure.
RO-50, one of the few remaining operational IJN
submarines, is surrendered.
Early November 1945:
Departs Kure for Sasebo with a skeleton crew of
a dozen officers and sailors. Arrives at Sasebo, moored in Ebisu Bay.
30 November 1945:
Removed from the Navy List.
1 April 1946: Operation "ROAD'S END":
RO-50 is stripped of all usable
equipment and material. She is scuttled 16 miles E of Kinai, Goto Islands.
 Author/historian Kimata Jiro suggests this was Sherman’s
TG 38.3. Author Ivan Musicant's "Battleship at War: The Epic Story of USS
WASHINGTON" mentions the attack. Lookouts on WASHINGTON sighted two torpedo
tracks passing ahead, one of which evidently had faulty steering. It appears
what Kimura heard was prematures or end-of-run explosions.
 Possibly USS TISDALE (DE-33). On 3 February 1945, while returning
to Manus on a round-trip convoy escort voyage, TISDALE attacked a sonar contact.
Special thanks go to Dr. Higuchi Tatsuhiro of Japan and to Brad Isherwood
for info on the events of 10/11 Feb 1945.
– Bob Hackett and Sander Kingsepp.
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